Fluid catalytic cracking (FCC) is primarily used to convert high boiling, high molecular weight hydrocarbons from petroleum into lower boiling, lower molecular weight compounds. The lower molecular weight compounds include gasoline, olefinic compounds, liquid petroleum gas (LPG), diesel fuel, etc., where the feedstock and the operating conditions can be adjusted to improve yields of a desired product. In an FCC apparatus, hydrocarbons are cracked with a catalyst in a riser, coke deposits on the catalyst in the riser, and the coke is burned in a regenerator to regenerate the catalyst. The catalyst is repeatedly cycled through the riser and regenerator during the cracking process.
FCC apparatuses typically include a stripper section that strips hydrocarbons from the spent catalyst before transferring the spent catalyst to the regenerator. The stripper is typically located at the bottom of a catalyst collection area for the riser. FCC apparatuses and the associated strippers are sized for target residence times and mass fluxes. Steam is supplied to the bottom of the stripper in sufficient volume to strip valuable hydrocarbon products from the catalyst via counter current flow, and also to fluidize the spent catalyst. Due to business reasons, sometimes the unit capacity and flow rate of catalyst to the stripper is lowered below the designed flow rate. When the catalyst flow rates decrease to a level much lower than the designed flow rates, higher steam to catalyst ratios are required to maintain sufficient stripping efficiency and to fluidize the catalyst in the stripper. The excess steam increases the gas and liquid load on equipment connected to the stripper. For example, the excess steam can increase the quantity of sour water produced per pound of hydrocarbon processed, as well as increase the operating costs for processing the excess steam. The reactor stripper is often filled with packing or distribution trays that distribute the spent catalyst as it flows through the stripper, and the excess volume of oversized strippers increases the capital costs for installing the packing or distribution trays.
Accordingly, it is desirable to provide FCC apparatuses and methods that require less steam to strip hydrocarbons from the spent catalyst in the stripper. In addition, it is desirable to provide FCC apparatuses and methods that reduce the cross sectional area and the volume of the stripper and thereby reduce the catalyst inventory and the packing or distribution trays in the stripper. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawing and this background.